Draft: Update README

README.md

@@ -2,14 +2,17 @@
 
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-JSONJ can be used to manipulate raw json input using _marks_ and custom _fragments generators_.
-* Library guarantees valid json output syntax;
-* Library doesn't validate output json semantic like unique keys.
+The library seeks for marks in input json and applies fragment generators, producing a new json. 
+It works with rules that are combinations or marks and generators.
+
+The library guarantees a valid output json syntax on valid input json. 
+Also, it is possible to generate a semantically invalid json if fragment generators are not correct. 
+For example, an incorrect fragment generator can produce duplicate object keys.
 
 ## Marks
 
-One can apply generator to  _marks_ of json input. Each _mark_ is json key name.
-For example, `uuid` and `id` maybe used as _mark_.
+Each _mark_ is an object key name. One can apply generator to _marks_ of input.
+For example, `uuid` and `id` can be used as _mark_.
 ```json
 [
     {
@@ -23,26 +26,26 @@ For example, `uuid` and `id` maybe used as _mark_.
 ]
 ```
 
-_Mark_ maybe renamed in result of _operation_.  It depends on `operation` mode and its rules.
+_Mark_ can be renamed in result of _operation_.  It depends on `operation` mode and its rules.
 
-Advice: wrap _marks_ by special chars, i.e. `__uuid__` and unwrap during `operation`.
+Advice: wrap _marks_ in special symbols, i.e. `__uuid__` and unwrap during `operation`.
 
 
 ## Operations
-Library supports number of operations, named _Mode_:
-  * `ModeInsert`: insert key/value pair after the _mark_.
-  * `ModeReplaceValue`: replace value, or convert it;
-  * `ModeReplace`: replace entire key/value pair;
+
+The library supports a number of operations, named _Mode_:
+  * `ModeInsert`: insert key/value pair after the _mark_,
+  * `ModeReplace`: replace the entire key/value pair,
+  * `ModeReplaceValue`: replace or convert value and keep key as is,
   * `ModeDelete`: delete key/value.
 
 ## Fragments generators
 
-Type `GenerateFragmentBatchFunc` describes interface of generators.
-Key feature of generators is batch processing. Batches speed up result output.
+Implement GenerateFragmentBatchFunc interface to create a custom fragment generator.
 
 Example:
 ```go
-// GeneratorParams customize generator behavior
+// GeneratorParams customizes generator behavior
 type GeneratorParams struct{
     EmbedObjectURL bool
     BaseURL        string
@@ -74,3 +77,5 @@ func Generator(ctx context.Context, iterator jsonj.FragmentIterator, p interface
     return result, nil
 }
 ```
+
+Batch processing is a key feature of generators. It speeds up the result output.